Robots in Antarctica Sea ice in the Antarctic is much thicker than previously thought, according to new data obtained by robotic submarines.

The findings, published today in the journal Nature Geoscience, will help researchers' efforts to understand the global effects of climate change.

Satellite images show sea ice coverage is in significant decline in the Arctic due to climate change, however paradoxically it's been increasing in the Antarctic, says the study's lead author Dr Guy Williams of the University of Tasmania.

"Sea ice is important in global climate studies, it's a modulator between ocean and atmosphere, it interacts with oceans because when salt water freezes it rejects salt, and it's a strong reflector of radiation and energy from the Sun," says Williams.

Satellite measurements of sea ice needs to be validated, and in Antarctica this has to date relied on shipboard observations and drilling.

These have suggested that the below-sea thickness of most Antarctic sea ice is less than a metre thick on average.

A whole new world

"These provided a new view of Antarctic sea ice with three dimensional maps, it's like going from a broken pair of binoculars to a band new telescope," says Williams.

"This is our first real look under the ice and it's a whole new world."

The authors found the average thickness of ice beneath sea level was 1.4 to 5.5 metres.

"We saw lots of ice more than five to eight metres thick, and a lot over 10 metres, and up to 17 metres in some places," says Williams.

Deformation

Williams says the research revealed the ice thickness was due to its "deformation", due to ice floes colliding, breaking apart and refreezing.

"We found that over half of the area of ice was heavily deformed, contributing to over three-quarters of the ice volume. This was sea ice that we've never been able to measure before, and possibly not related to what we're seeing on the surface."

The findings will help scientists develop more accurate models that better reflect the counterintuitive Antarctic sea ice pattern currently unfolding.

Two cruises

The study was conducted over two cruises involving the submarines. The first was in 2010 covered the Bellingshausen Sea continental shelf and the North-west Weddell Sea continental slope, while the second, in 2012, used the Aurora Australis to examine East Antarctica offshore from Wilkes Land.

The submarine uses a multi-beam sonar to map the bottom of the ice and has a 10 hour range, working autonomously on a pre-programmed course before returning to ship.

"It operates in a classic mow the lawn pattern, similar to aerial and sea floor surveys," says Williams.